It is known to provide such registers having a plurality of vanes (blades, slats, flaps) which are synchronised under a common control, in the manner described for example in international patent specification No. W096116827. These pivoting vanes are usually articulated about their central axis of symmetry, and are therefore driven simultaneously, all in the same direction, by a suitable drive mechanism such as a crank.
The use of a register of this kind makes it necessary to introduce a lateral component into the air flow, which is thereby offset upwardly or downwardly with respect to the structure which carries the vanes. With this arrangement it is only when the register is fully open that the air flow is properly homogeneous. Thus, in all intermediate positions between the fully closed and fully open positions of the register, there is a tendency towards poor mixing of the air, for example at the surface of a heat exchanger or in a mixing chamber, both of which are situated downstream of the multi-vane register.